Assessment Comments
Assessment is based on results of IDNR/UHL monthly ambient city monitoring conducted upstream from Spencer from 2002-04 and 2003 IDNR/UHL REMAP sampling: FIBI = 28 (fair), BMIBI = 47 (fair). FIBI BIC = 43; BMIBI BIC = 54.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (evaluated) as "partially supported" based on results of IDNR/UHL REMAP sampling conducted in 2003. The assessment is considered evaluated because of equipment failure by staff gathering the fish data. The equipment failure led to the use of only one backpack shocker on the site which averaged 63 feet in width. The partial support applies because the FIBI score failed to meet the FIBI BIC for this ecoregion. However, the results from IDNR/UHL monthly ambient chemical/physical water quality monitoring conducted upstream from Spencer at the County Road M-38 bridge southwest of Spencer from January 2002 through December 2004 (STORET station 10210001 (formerly station 924003)) suggest this segment is "fully supporting" the aquatic life use.
EXPLANATION: The assessment was primarily based on data collected in 2003 as part of the DNR/UHL stream REMAP project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2003 FIBI score was 28 (fair) and the BMIBI score was 47 (fair). The aquatic life use support was assessed (evaluated - see above) as partially supporting (= PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54.
Conversely, the monitoring at the IDNR/UHL city station upstream from Spencer showed no violations of Class B(LR) water quality criteria during the 2002-2004 assessment period for dissolved oxygen (minimum value = 5.7 mg/l), pH (range = 7.7 to 8.6 units), or ammonia-nitrogen (maximum value = 0.44) in the 36 samples analyzed. In addition, levels of toxic metals in the 32 samples analyzed, and levels of pesticides in the seven samples analyzed, were all below Class B(LR) chronic criteria. These results suggest "full support" of the Class B(LR) aquatic life uses.
